Generally, known sensing methods for measuring pressure include, besides a sensing system using a strain-resistant element, a sensing system using a capacitance element. According to the sensing system using a capacitance element, the structure of a sensor element is simpler than that of a sensor element in the sensing system using a strain-resistant element. Thus, the sensing system using a capacitance element has an advantage of being capable of inexpensively producing the sensor element, without the use of a semiconductor production process which requires a high production cost.
For example, touch sensors disclosed in Non-Patent Documents 1 and 2 are known as the sensing system using a capacitance element. Each of the touch sensors is a pressure sensor including capacitance elements arranged in an arrayed manner on its sensing surface, and is thus suitable for measurement of pressure fluctuating waveform.
The following description deals in detail with the touch sensor disclosed in Non-Patent Document 2. FIG. 26 is an outline perspective view of a pressure detection section in the touch sensor disclosed in Non-Patent Document 2. FIG. 27 is an exploded perspective view of the pressure detection section illustrated in FIG. 26. FIG. 28 (a) is a top plan view of the pressure detection section illustrated in FIG. 26. FIG. 28 (b) is a view illustrating a layout of capacitance elements in the pressure detection section. FIG. 29 is a circuit diagram of the touch sensor including the pressure detection section illustrated in FIG. 26.
As illustrated in FIGS. 26 and 27, a touch sensor 1E disclosed in Non-Patent Document 2 mainly includes: lower electrodes 11; upper electrodes 21; and spacer members 31. The lower electrodes 11 are made up of a plurality of strip-shaped copper foil electrodes which are provided in rows so as to substantially linearly extend in parallel with one another. The upper electrodes 21 are made up of a plurality of strip-shaped copper foil electrodes which are provided in columns so as to substantially linearly extend in parallel with one another. The upper electrodes 21 are disposed in a direction at right angles to the direction in which the lower electrodes 11 are disposed. The lower electrodes 11 and the upper electrodes 21 are separated from each other by the spacers 31 made of silicon rubber.
At intersections of the lower electrodes 11 and the upper electrodes 12, both of which are arranged in a matrix manner, portions of the lower electrodes 11 and portions of the upper electrodes 21 are disposed a predetermined distance apart from each other due to the spacers 31 such that the portions face each other, respectively. This allows capacitance elements 41 (see FIG. 28 (a)), each serving as a sensor element, to be formed at the intersections, respectively.
As illustrated in FIGS. 28 (a) and 28 (b), in the touch sensor 1E having the above arrangement, the capacitance elements 41 are arranged in an arrayed manner when the pressure detection section is observed from above. Respective capacitances of the capacitance elements 41 are changed in response to pressure which causes the upper electrodes 21 or the lower electrodes 11 to strain in a direction in which the upper electrodes 21 and the lower electrodes 11 become closer to each other.
In view of this, it is possible to obtain, by adopting a circuitry illustrated in FIG. 29, the capacitance of a specific one of the capacitance elements 41 arranged in an arrayed manner. Specifically, according to the circuitry, ones of the lower electrodes 11 and the upper electrodes 21, which are arranged in a matrix manner, are connected with a power supply 60 via a multiplexer 50, and the other ones of the lower electrodes 11 and the upper electrodes 21 are connected with a detector 70 also via a multiplexer 50. With the circuitry, when the multiplexers 50 select a specific one of the lower electrodes 11 and a specific one of the upper electrodes 21, the specific one of the capacitance elements 41 is identified and the capacitance of the specific capacitance element 41 thus identified is obtained through the detector 70. More specifically, for example, as in FIG. 29, in a case where (i) a specific lower electrode 11 in the second row from the top and (ii) a specific upper electrode 21 in the third column from the left are selected, the capacitance of a specific capacitance element indicated by the reference numeral 42 is outputted. Consequently, it is possible to measure pressure applied to any point on the sensing surface of the touch sensor 1E.
Known as other arts for measuring pressure fluctuating waveform are a surface pressure distribution sensor, disclosed in Patent Document 1, which uses a capacitance element, and a pressure pulse wave sensor and a pressure pulse wave analyzation apparatus described in Patent Document 2, both of which use a piezoelectric sheet.
FIG. 30 is a view illustrating a schematic arrangement of the surface pressure distribution sensor of Patent Document 1. As illustrated in FIG. 30, a surface pressure distribution sensor 101 includes a row wiring section 11 and a column wiring section 12. The row wiring section 11 and the column wiring section 12 are provided a predetermined distance apart from each other via a spacer 18 so as to face each other. The row wiring section 11 includes: a glass substrate 13; a lot of row wires 14 on the glass substrate 13; and an insulating film 15 covering the row wires 14. The row wires 14 are provided in parallel with one another in a first direction. The column wiring section 12 includes: a flexible film 16; and a lot of column wires 17 on the flexible film 16. The column wires 17 are provided in parallel with one another in a second direction.
FIG. 31 is a view illustrating a schematic arrangement of the pressure pulse wave sensor of Patent Document 2. As illustrated in FIG. 31, a pressure pulse wave sensor 102 is formed so that a first sensor section 12 and a second sensor section 14 are stacked. The first sensor section 12 includes a plurality of strip-shaped piezoelectric sheets 16 and a flexible sheet 18. The plurality of piezoelectric sheets 16 are arranged in a width direction of the piezoelectric sheets 16, and are integrally fixed to the flexible sheet 18. The piezoelectric sheets 16 are fastened to a body surface so as to detect pulse waves of the living body. The second sensor section 14 has the same structure as the first sensor section 12, and is rotated in a horizontal plane by 90 degrees with respect to the first sensor section 12.
[Non-Patent Document 1]
R. S. Fearing, “Tactile Sensing Mechanisms”, The International Journal of Robotics Research, June 1990, Vol. 9, No. 3, pp. 3-23
[Non-Patent Document 2]
D. A. Kontarinis et al., “A Tactile Shape Sensing and Display System for Teleoperated Manipulation”, IEEE International Conference on Robotics and Automation, 1995, pp. 641-646
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 317403/2004 (Tokukai 2004-317403; published on Nov. 11, 2004)
[Patent Document 2]
Japanese Unexamined Patent Application Publication No. 208711/2004 (Tokukai 2004-208711; published on Jul. 29, 2004)